1. Field of the Invention
The present invention relates generally to methods to reduce the incidence of Intraventricular Hemorrhage (IVH) in preterm infants. The present invention also relates to the supplementation with docosahexaenoic acid and arachidonic acid of infant formulas designed for preterm infants.
2. Description of Related Art
Intraventricular Hemorrhage (IVH), a bleeding from fragile blood vessels in the brain, is a significant cause of morbidity and mortality in premature infants and may have life-long neurological consequences such as cerebral palsy, mental retardation, and seizures. These vessels are especially fragile in preterm infants, particularly those born more than 8 weeks early, i.e., before 32 weeks of gestation. IVH is more commonly seen in extremely premature infants; its incidence is over 50% in preterm infants with birth weight less than 750 grams, and up to 25% in infants with birth weight less than 1000 to 1500 grams.
IVH encompasses a wide spectrum of intra-cranial vascular injuries with bleeding into the brain ventricles, a pair of C-shaped reservoirs, located in each half of the brain near its center, that contain cerebrospinal fluid. The bleeding occurs in the subependymal germinal matrix, a region of the developing brain located in close proximity to the ventricles. Within the germinal matrix, during fetal development, there is intense neuronal proliferation as neuroblasts divide and migrate into the cerebral parenchyma. This migration is about complete by about the 24th week of gestation, although glial cells can still be found within the germinal matrix until term. The germinal matrix undergoes rapid involution from the 26th to the 32nd week of gestation, at which time regression is nearly complete, as glial precursors migrate out to populate the cerebral hemispheres.
Supporting this intense cell differentiation and proliferation activity there is a primitive and fragile capillary network. These vessels have thin walls for their relatively large size, lack a muscularis layer, have immature interendothelial junctions and basal laminae, and often lack direct contact with perivascular glial structures, suggesting diminished extravascular support. It is in this fragile capillary network where IVH originates. When a fetus is born prematurely, the infant is suddenly thrust from a well-controlled, protective environment into a stimulating, hostile one. Because of this physiologic stress and shock, the infant may lose the ability to regulate cerebral blood flow and may suffer alterations in blood flow and pressure and in the amounts of substances dissolved in the blood such as oxygen, glucose and sodium. The fragile capillaries may, and often do, rupture.
The severity of the condition depends on the extent of the vascular injury. There are four grades, or stages, of IVH as can be seen using ultrasound or brain computer tomography. Grade I IVH, the less severe stage, involves bleeding in the subependymal germinal matrix, with less than 10% involvement of the adjacent ventricles. Grade II IVH results when 10 to 40% of the ventricles are filled with blood, but without enlargement of the ventricles. Grade III IVH involves filling of over 50% of the ventricles with blood, with significant ventricular enlargement. In Grade IV IVH, the bleeding extends beyond the intraventricular area into the brain parenchyma (intraparenchymal hemorrhage).
The major complications of IVH relate to the destruction of the cerebral parenchyma and the development of posthemorrhagic hydrocephalus. Following parenchymal hemorrhages (Grade IV IVH), necrotic areas may form cysts that can become contiguous with the ventricles. Cerebral palsy is the primary neurological disorder observed in those cases, although mental retardation and seizures may also occur. In addition, infants affected with Grade III to IV IVH may develop posthemorrhagic hydrocephalus, a condition characterized by rapid growth of the lateral ventricles and excessive head growth within two weeks of the hemorrhage. Likely causes are obstruction of the cerebrospinal fluid conduits by blood clots or debris, impaired absorption of the cerebrospinal fluid at the arachnoid villi, or both. Another form of the hydrocephalus condition may develop weeks after the injury. In this case the likely cause is obstruction of the cerebrospinal fluid flow due to an obliterative arachnoiditis in the posterior fossa.
There is no specific treatment of IVH once it develops. Surgery will not prevent or cure the bleeding. Treatment of hydrocephalus may require use of spinal taps, ventricular reservoirs, or ventricular peritoneal shunts. A spinal tap is used to remove fluid from the spinal canal to reduce pressure. A needle is inserted in the infant""s back to let fluid drip out. The procedure may allow time for the blood clots to clear by themselves and the fluid conduits to clear up. If the blockage is so severe that the fluid cannot circulate from the ventricles to the spinal canal, tubing can be surgically implanted into the ventricles (ventricular reservoirs). If the condition persists, a permanent tubing (shunt) can be placed in the ventricles. One end ot the tubing is placed in a ventricle, and the other is placed into the abdominal cavity. The tubing is tunneled under the skin.
Prevention of IVH is, thus, the favored approach. Prevention of prematurity, optimal management of labor and delivery, and the administration to mothers at risk of early delivery of drugs such as corticosteroids and phenobarbital are some of the methods of prenatal intervention aiming to reduce the incidence of IVH. Postnatal intervention on the premature infant is also possible. For example, indomethacin may be administered, a few hours after birth, to those premature infants that are at high risk of developing IVH. Indomethacin inhibits the formation of prostaglandins by decreasing the activity of the cyclooxygenase, may cause the maturation of the germinal matrix microvasculature, and is associated with decreased cerebral blood flow. Its use, however, is controversial as it may cause acute renal failure and other serious side effects.
Thus, there is a present need for a method to reduce the incidence of Intraventricular Hemorrhage in preterm infants. The method must not negatively affect growth pattern, must be safe to be administered to infants, and, if administered as part of the nutritional intake of the infants, this feeding must be well tolerated by the infants.
It is now known in the art that polyunsaturated fatty acids (PUFA) of both the n-3 and n-6 families are required for normal growth and development. See Innis, S. M. et al., Prog Lipid Res 1991; 30:39-103; see also Neuringer, M. and Conner, W. E. Nutr Rev 1986; 44:285-294. The n-3 long chain polyunsaturated fatty acid (LCPUFA), docosahexaenoic acid (DHA, 22:6n-3) is required for optimal brain, neural, and retinal development (See Innis et al. (1991), opus cit.; see also Neuringer and Connor (1986), opus cit.) and the n-6 LCPUFA arachidonic acid (ARA, 20:4n-6) is needed to support good growth and development (See Carlson, S. E. et al., Am J Clin Nutr 1993; 58:35-42). Infants who are breast-fed receive these LCPUFA in their diet because human milk contains low levels of DHA and ARA. While the amounts of DHA and ARA in human milk vary among individual women and populations depending upon maternal diets, studies across many population groups have shown the median levels of DHA and ARA in human milk to be approximately 0.3% and 0.5-0.6% of total fatty acid content, respectively. See Innis, S. M., J Pediatr 1992; 120:S56-61; see also Koletzko, B. et al., J Pediatr 1992; 120:S62-70.
Infant formulas currently marketed in the United States did not until recently contain any preformed DHA or ARA. Thus, infants solely fed these infant formulas ingest no DHA or ARA. The formulas do, however, contain the 18-carbon chain length essential fatty acids, alpha linolenic (linolenic) acid (ALA, 18:3n-3) and linoleic acid (LA, 18:2n-6), at levels equal to or greater than the levels present in most human milks (Innis 1992). Infants can synthesize the n-3 and n-6 LCPUFA, DHA and ARA, from these 18-carbon precursor fatty acids (linolenic and linoleic acid, respectively) by a series of metabolic steps requiring desaturation and elongation. See Carnielli, V. P. et al., Pediatr Res 1996; 40:169-174; see also Salem, N. et al., Proc Natl Acad Sci 1996; 93:49-54; see also Sauerwald, T. U. et al., Pediatr Res 1997; 41:183-187. It is not clear, however, whether all infants, especially preterm infants, are capable of synthesizing enough DHA and ARA from the precursors, linolenic and linoleic acids, to meet their growth and development needs.
Diersen-Schade et al. (in: Riemersma, R. et al. (editors), Essential Fatty Acids and Eicosanoids: Invited Papers from the Fourth International Congress, p. 123-7 (1998)) examined the safety and effects of feeding relatively healthy preterm infants, formulas supplemented with just DHA or DHA and ARA sourced from the single cell Martek oils, DHASCO(copyright) and ARASCO(copyright), at the median levels found in human milk. See Koletzko et al. (1992), opus cit. That study was designed to feed relatively healthy preterm infants for at least twenty-eight days after the start of enteral feeds with one of three study formulas: a Control formula with no DHA or ARA, a formula supplemented with DHA, or a formula supplemented with DHA and ARA.
After twenty-eight days, the subjects were fed a commercial cow""s milk based, routine formula. The subjects were followed up to 57 Weeks Postmenstrual Age (PMA). Results from that study were intriguing. Even though the preterm subjects had been fed the study formulas for only twenty-eight days, differences in weight gains and mean achieved weights were detected for the DHA+ARA supplemented group compared to the Control group. For the twenty-eight day study period during which the study formulas were ingested, subjects in the DHA+ARA supplemented group gained more weight than the subjects in the Control group. At 48 Weeks PMA, subjects in the group supplemented with DHA and ARA had a greater mean achieved weight than that for the Control group or the group supplemented with DHA only. The mean weight of the group supplemented with DHA and ARA was also not significantly different from that of a reference term infant group that had been exclusively fed with human milk. By 57 Weeks PMA, the mean weight of the group supplemented with DHA and ARA was no longer significantly different than the other two formula groups. This DHA and ARA supplemented group was, however, the only formula group with a mean weight not significantly less than that of the human milk fed term infants.
The Diersen-Schade et al. (1998), opus cit. study showed that the formula, supplemented with DHA and ARA at median levels found in human milk, had benefited the preterm infants with an earlier phase of catch-up growth even though the supplementation was administered for a short (twenty-eight days) period. The study raised the need for a long-term feeding study in premature infants to determine: 1) if such long-term feeding of these LCPUFA was safe, and 2) if the growth benefits would be even more enhanced by a longer feeding period.
In addition, the study should include infants who are not, xe2x80x9crelatively healthyxe2x80x9d to mirror preterms as they are found in actual clinical practice. This approach would mean a study population with multiple concomitant medical conditions related to prematurity. Because the study population would be less healthy than the preterm subjects in the Diersen-Schade et al. study, and because there is a concern among some nutritional scientists that formulas supplemented with DHA and ARA may increase the risk of the preterm infant for greater morbidity, the subjects would have to be tracked, especially in the early hospitalization period, for concomitant medical conditions common in the postnatal course of preterm infants, such as necrotizing enterocolitis (NEC), retinopathy of prematurity (ROP), sepsis, bronchopulmonary dysplasia (BPD), and intraventricular hemorrhage (IVH), with or without hydrocephalus. IVH would be of special significance as there is some concern that supplementation with long chain omega-3 PUFA might lead to increased bleeding or increased incidence or severity of IVH.
It has now been discovered through the present invention that the administration to very low birth weight (VLBW) premature infants of a combination of docosahexaenoic acid (DHA) and arachidonic acid (ARA) from a source that is substantially free of eicosapentaenoic acid (EPA) reduces the incidence of IVH in those infants and results in nonspecific low blood pressure readings in those infants. These surprising discoveries are a consequence of a study conducted to determine the effect of feeding DHA- and ARA-supplemented infant formulas to VLBW infants on the infants"" growth.
In addition to discovering that supplementation of infant formulas with long chain omega-3 PUFA does not lead to increased bleeding (See Heird, W. C., Lipids 1999; 34:207-214) which could lead to increased incidence or severity of IVH, when the source of omega-3 PUFA is substantially free of EPA, the VLBW infants fed with the supplemented formula show a reduced incidence of IVH. Thus, the present invention surprisingly addresses the need for a method to reduce the incidence of Intraventricular Hemorrhage in preterm infants. The method does not negatively affect growth pattern, is safe to be administered to infants, and, if administered as part of the nutritional intake of the infants, this feeding is well tolerated by the infants.
The present invention is directed to a novel method to reduce the incidence of Intraventricular Hemorrhage in preterm infants. This novel method comprises administering the infants with an effective amount of docosahexaenoic acid and arachidonic acid substantially free of eicosapentaenoic acid. The LCP fatty acids may be administered using a DHA- and ARA-supplemented formula. The formula does not negatively alter growth patterns, is well tolerated and imposes no safety issues.
The present invention relates to a method of reducing the incidence of Intraventricular Hemorrhage in preterm infants. The method comprises administering to those infants a combination of DHA and ARA, substantially free of eicosapentaenoic acid (EPA).
In one embodiment of the invention, the combination of DHA and ARA is administered as part of an infant formula. The infant formula for use in the present invention is, typically, nutritionally complete and contains suitable types and amounts of lipids, carbohydrates, proteins, vitamins and minerals. The amount of lipids or fats typically can vary from about 3 to about 7 g/100 kcal. The amount of proteins typically can vary from about 1 to about 5 g/100 kcal. The amount of carbohydrates typically can vary from about 8 to about 14 g/100 kcal. Protein sources can be any used in the art, e.g., nonfat milk, whey protein, casein, soy protein, hydrolyzed protein, and amino acids. Lipid sources can be any used in the art, e.g., vegetable oils such as palm oil, soybean oil, palm olein oil, coconut oil, corn oil, canola oil, low erucic acid rapeseed oil, sunflower oil, safflower oil, medium chain triglyceride oils, high oleic sunflower oil, and high oleic safflower oil. Carbohydrate sources can be any known in the art, e.g., lactose, glucose polymers, corn syrup solids, maltodextrins, sucrose, starch, and rice syrup solids. Conveniently, several commercially available infant formulas can be used. For example, Enfamil(copyright) Premature Formula, EnfaCare(copyright), and Enfamil(copyright) With Iron (all available from Mead Johnson and Company, Evansville, Ind., U.S.A.) may be supplemented with suitable levels of ARA and DHA at the proper ratios and used to practice the method of the present invention. Particular infant formulas suitable for use in the present invention are described in the Example.
The form of administration of DHA and ARA in the method of the present invention is not critical, as long as an effective amount is administered. Most conveniently, DHA and ARA are supplemented into an infant formula to be fed to the infants after the infants receive their first enteral feeding. Alternatively, DHA and ARA can be administered as a supplement not integral to formula feeding, for example, as oil drops, sachets or in combination with other nutrients such as vitamins.
The method of the invention requires a combination of DHA and ARA. The weight ratio of ARA:DHA is typically from about 1:3 to about 9:1. In one embodiment of the present invention, this ratio is from about 1:2 to about 4:1. In yet another embodiment, the ratio is from about 2:3 to about 2:1. In one particular embodiment the ratio is about 2:1.
The effective amount of DHA for use in the present invention is typically from about 3 mg per kg of body weight per day to about 150 mg per kg of body weight per day. In one embodiment of the invention, the amount is from about 6 mg per kg of body weight per day to about 100 mg per kg of body weight per day. In another embodiment the amount is from about 10 mg per kg of body weight per day to about 60 mg per kg of body weight per day. In yet another embodiment the amount is from about 15 mg per kg of body weight per day to about 30 mg per kg of body weight per day.
The effective amount of ARA for use in the present invention is typically from about 5 mg per kg of body weight per day to about 150 mg per kg of body weight per day. In one embodiment of this invention, the amount varies from about 10 mg per kg of body weight per day to about 120 mg per kg of body weight per day. In another embodiment, the amount varies from about 15 mg per kg of body weight per day to about 90 mg per kg of body weight per day. In yet another embodiment, the amount varies from about 20 mg per kg of body weight per day to about 60 mg per kg of body weight per day.
The amount of DHA in infant formulas for use in the present invention typically varies from about 5 mg/100 kcal to about 80 mg/100 kcal. In one embodiment of the present invention it varies from about 10 mg/100 kcal to about 50 mg/100 kcal; and in another embodiment from about 15 mg/100 kcal to about 20 mg/100 kcal. In a particular embodiment of the present invention, the amount of DHA is about 17 mg/100 kcal.
The amount of ARA in infant formulas for use in the present invention typically varies from about 10 mg/100 kcal to about 100 mg/100 kcal. In one embodiment of the present invention, the amount of ARA varies from about 15 mg/100 kcal to about 70 mg/100 kcal. In another embodiment the amount of ARA varies from about 20 mg/100 kcal to about 40 mg/100 kcal. In a particular embodiment of the present invention, the amount of ARA is about 34 mg/100 kcal.
The infant formula supplemented with oils containing DHA and ARA for use in the present invention can be made using standard techniques known in the art. For example, they can be added to the formula by replacing an equivalent amount of an oil, such as high oleic sunflower oil, normally present in the formula. As another example, the oils containing DHA and ARA can be added to the formula by replacing an equivalent amount of the rest of the overall fat blend normally present in the formula without DHA and ARA.
The source of DHA and ARA can be any source known in the art as long as it is substantially free of EPA. In one embodiment of the present invention, sources of DHA and ARA are single cell oils as taught in U.S. Pat. Nos. 5,374,567; 5,550,156; and 5,397,591, the disclosures of which are incorporated herein in their entirety by reference. However, the present invention is not limited to only such oils. DHA and ARA can be in natural form provided that the remainder of the LCP source is substantially free of EPA and does not result in a deleterious effect on the infant. Alternatively, DHA and ARA can be used in refined form. The LCP source used in the present invention is substantially free of EPA. For example, in one embodiment of the present invention the infant formula contains less than about 16 mg EPA/100 kcal; in another embodiment less than about 10 mg EPA/100 kcal; and in yet another embodiment less than about 5 mg EPA/100 kcal. One particular embodiment contains substantially no EPA. Another embodiment is free of EPA in that even trace amounts of EPA are absent from the formula.